1. Field of the Invention
The present invention relates to a battery technology and more particularly to a technology which is adaptable for a nonaqueous lithium secondary battery, a positive electrode material thereof, and the like.
2. Description of the Related Art
The inventors investigated the following technologies when the inventors created the present invention. The technologies are briefly described below.
A conventional nonaqueous lithium secondary battery uses lithium cobaltate, lithium manganate and lithium nickelate for the positive electrode thereof. The theoretical capacity of the battery per active material weight was 137 mAh/g, 148 mAh/g, and 198 mAh/g, and has never exceeded 200 mAh/g.
To cope with this capacity problem, study has been made to use a vanadium pentoxide material, having many valences and capability to give a high capacity, for a positive electrode material of a lithium secondary battery. However, a lithium ion source is not contained in the positive electrode material, that is, lithium ions must be supplied in the negative electrode material. Accordingly, its application is limited to a primary battery or a secondary battery of a very low current amount.
When the crystalline vanadium pentoxide is used for the positive electrode material, a low valent vanadium is used in order to give a high capacity to the positive electrode. In the case, however, the following problem arises: The charging and discharging operation causes the crystal structure to collapse, and thereby the repetition of the charge/discharge cycle lowers the battery capacity gradually.
JP-A-5-105450 discloses an approach to make the vanadium pentoxide an amorphous for the purpose of preventing such a crystal structure from collapsing.
JP-A-5-198300 discloses a constitution using γ type LiV2O5 for the positive electrode active material which allows lithium ions to be easily intercalated and deintercalated. The publication describes that the γ type LiV2O5 is formed by baking vanadium pentoxide and a lithium salt.
After investigating the publications, the inventors have found that the positive electrode active material using the vanadium pentoxide has the following disadvantages.
In the inventions disclosed in the publications mentioned above, the improvement of the property of the vanadium pentoxide as the electrode active material is based the crystal structure of the vanadium pentoxide. However, the effect of the improvement is not still satisfactory.